1. Field of the Invention
The present invention relates to a camera of the kind which measures light with a light measuring field divided into a plurality of areas.
2. Description of Related Art
Various kinds of cameras have been provided that divide a photo-taking field into a plurality of areas and appositely perform an exposure action on a photo-taking image plane using a luminance signal obtained for each of the divided areas. For example, a camera disclosed in Japanese Laid-Open Patent Application No. HEI 3-223825 is arranged to detect luminance for every one of a plurality of light measuring areas, to select at least one focus detecting area from among a plurality of focus detecting areas for which focus is detectable independent of each other, to group a plurality of light measuring areas in a circular shape around and coaxially with the selected focus detecting area and to compute a measured light value of the whole photo-taking field by variably weighting the average luminance value of these grouped light measuring areas.
Another camera disclosed in Japanese Laid-Open Patent Application No. HEI 5-53169 is arranged to obtain an object position within a photo-taking field by detecting, for example, the position of the visual line of the camera operator, to divide and group many pixels (picture elements) of a light measuring CCD image sensor into a plurality of patterns in accordance with a dividing pattern which is flexibly variable according to the object position detected, and to obtain a measured light value by weighting the average luminance value of each of these pattern groups.
In order to take a shot with an amount of exposure most apposite to a photo-taking field, it is a trend to obtain luminance information as much as possible from the photo-taking field by dividing the areas of a light measuring sensor into many areas. Divided light measuring patterns most apposite to a photo-taking object is obtainable using an area sensor such as a CCD in a manner, for example, as disclosed in the above Japanese Laid-Open Patent Application No. HEI 5-53169. However, the area sensor is not only expensive but also has a drawback with respect to its response for a low luminance object, because it is an electric-charge storing type sensor. In view of this drawback, a light measuring sensor of photodiode type is widely in use.
However, an increase in the number of divisions of the photodiode-type light measuring sensor results in a smaller light receiving area of each divided area. The smaller light measuring area eventually lowers the light measuring ability of the light measuring sensor.
Therefore, a light measuring sensor having some number of divided parts of certain sizes can generally be considered to be more easily usable with respect to the light measuring capability for a low luminance and capability for a light measuring arithmetic process than the use of, as a light measuring sensor, an area sensor composed of an aggregation of minute pixel sensors in which many finely divided patterns can be arbitrarily formed.
Meanwhile, cameras are arranged to perform a focus detecting action for the purpose of adjusting the focus of a photo-taking lens to a photo-taking object. It is also a general trend to divide a focus detecting sensor used for this purpose into many parts, or areas. With two area sensors employed for this purpose, for example, the focus for many areas within a photo-taking image plane can be detected by dividing pixels of these area sensors and by obtaining correlation between the divided pixels according to a known phase-difference detecting method.
As regards known methods for arranging cameras with respect to the relation between a light measuring area and a distance measuring area (focus detecting area), such as the camera disclosed in the above Japanese Laid-Open Patent Application No. HEI 3-223825, these cameras are arranged to have a fewer number of focus detecting areas than the number of light measuring areas. Therefore, it is possible to set each focus detecting area approximately in a barycenter position of the light measuring area which includes that focus detecting area. In the case of each of these cameras, therefore, an approximately apposite exposure can be made by carrying out a light measuring arithmetic operation with some suitable weighting on the assumption that a light measuring area corresponding to a focus detecting area for which focus is to be detected corresponds to the position of a main photo-taking object.
However, in a case where a camera is arranged to have a number of divided focus detecting areas equal to or more than that of light measuring areas, it becomes difficult to set a focus detecting area where a focusing action is to be performed on a main photo-taking object approximately in the barycenter position of a light measuring area. In such a case, it becomes difficult to select only one of the light measuring areas corresponding to a main photo-taking object position on which a light measuring arithmetic operation is to be carried out. Thus, it becomes impossible to accurately determine an exposure setting for the photo-taking object because of an optical discrepancy.
Such an optical discrepancy which is, so to speak, the parallax of a focus detecting area and a light measuring area, results from a discrepancy in shape of sensor layout between a focus detecting sensor and a light measuring sensor or from a problem related to optical arrangement. FIG. 3 shows, by way of example, such a discrepancy. In the case of FIG. 3, focus detecting areas 71, 73, 75 and 77, which are included in a group of focus detecting areas 70 to 78, are respectively located on boundaries of a plurality of light measuring areas S0 to S4.
In accordance with an aspect of the invention, in a camera in which a plurality of light measuring areas and a plurality of focusing detecting areas are provided, and a particular light measuring area to be subjected to a large weighting is selected according to selection of one of the focus detecting areas, if a focus detecting area located on a boundary between light measuring areas is selected, the particular light measuring area to be subjected to a large weighting is selected using focus detecting states of other focus detecting areas adjacent to the selected focus detecting area.